JP7552080B2 - Precipitation hardening stainless steel powder, compound, granulated powder, precipitation hardening stainless steel sintered body, and method for manufacturing the precipitation hardening stainless steel sintered body - Google Patents

Description

The present invention relates to precipitation hardening stainless steel powder, compounds, granulated powders, precipitation hardening stainless steel sintered bodies, and methods for producing precipitation hardening stainless steel sintered bodies.

In powder metallurgy, a composition containing metal powder and an organic binder is molded into a desired shape, the resulting molded body is degreased to produce a degreased body, and the degreased body is then fired to produce a sintered body. In the process of producing such a sintered body, atomic diffusion occurs between the particles of the metal powder, which causes the molded body to gradually become dense and sintered.

In this type of powder metallurgy process, when the compact is degreased, the compact is heated to thermally decompose the organic binder and remove it. If the organic binder remains in the compact, the properties of the sintered compact will deteriorate, so various methods for removing the organic binder are being investigated.

For example, Patent Document 1 discloses that a molded body containing a metal material powder and a binder containing polyoxymethylene resin is degreased by heating it in an acid-containing atmosphere. By carrying out the degreasing process in this manner in an acid-containing atmosphere, the acid decomposes the binder, allowing the binder to be removed efficiently. This reduces the aforementioned problems.

Japanese Patent Application Publication No. 4-247802

In the method described in Patent Document 1, it is believed that most of the organic binder is removed in the degreasing process. However, some of the organic binder remains in the molded body and is removed in the subsequent firing process as the sintering of the metal material powder progresses. At this time, for example, when the particle size of the metal material powder used is small, the sintering tends to progress faster. In other words, sintering may start at a lower temperature. If this happens, the organic binder may be trapped inside the molded body during the firing process. As a result, the carbon atom concentration in the sintered body increases, and there is a concern that the mechanical properties of the sintered body may deteriorate.

The precipitation hardening stainless steel powder according to the application example of the present invention is
Cr is contained at a concentration A in the range of 15.00 mass% or more and 17.50 mass% or less,
Si is contained at a concentration B in the range of 0.30 mass% or more and 1.00 mass% or less,
Nb is contained at a concentration C in the range of 0.15 mass% or more and 0.45 mass% or less,
Ni is contained at a concentration D in the range of 3.00 mass% or more and 5.00 mass% or less,
Mn is contained at a concentration E in the range of 0.05 mass% or more and 1.00 mass% or less,
Cu is contained at a concentration F in the range of 3.00 mass% or more and 5.00 mass% or less,
The value of δ defined by the following formula (1) is 10.0 mass % or more and 13.5 mass % or less.
δ=3(A+1.5B+0.5C)-2.8(D+0.5E+0.5F)-19.8・
...(1)

1 is a process diagram showing a method for producing a precipitation hardening stainless steel sintered body according to an embodiment. FIG.

The following provides a detailed description of embodiments of the precipitation hardening stainless steel powder, compound, granulated powder, precipitation hardening stainless steel sintered body, and method for producing the precipitation hardening stainless steel sintered body of the present invention.

1. Precipitation hardening stainless steel powder First, the precipitation hardening stainless steel powder according to the embodiment will be described.

In powder metallurgy, a composition containing metal powder and a binder is molded into the desired shape, and then degreasing and sintering are performed to obtain a sintered body of the desired shape. Compared to other techniques, this type of powder metallurgy makes it possible to manufacture sintered bodies of complex and fine shapes in near-net shapes, i.e., shapes that are close to the final shape.

The precipitation hardening stainless steel powder according to the embodiment is a powder composed of precipitation hardening stainless steel containing Cr, Si, Nb, Ni, Mn and Cu. In this powder, Cr is contained at a concentration A in the range of 15.00 mass% to 17.50 mass%, Si is contained at a concentration B in the range of 0.30 mass% to 1.00 mass%, Nb is contained at a concentration C in the range of 0.15 mass% to 0.45 mass%, Ni is contained at a concentration D in the range of 3.00 mass% to 5.00 mass%, Mn is contained at a concentration E in the range of 0.05 mass% to 1.00 mass%, and Cu is contained at a concentration F in the range of 3.00 mass% to 5.00 mass%. In this powder, the value of δ defined by the following formula (1) is 10.0 mass% to 14.0 mass%.

δ=3(A+1.5B+0.5C)-2.8(D+0.5E+0.5F)-19.8... (1)

With such a precipitation hardening stainless steel powder, it is possible to suppress sinterability while maintaining the excellent mechanical strength derived from precipitation hardening stainless steel. Therefore, the temperature at which sintering starts can be increased in the firing process. As a result, the organic binder remaining in the compact can be more reliably removed, and an increase in the carbon atom concentration in the sintered body can be suppressed. Therefore, the precipitation hardening stainless steel powder according to the embodiment makes it possible to produce a sintered body with high mechanical strength.

The alloy composition of the precipitation hardening stainless steel powder according to the embodiment will be described in more detail below. In the following description, the precipitation hardening stainless steel powder may also be simply referred to as "metal powder."

1.1 Cr
Cr (chromium) is an element that mainly imparts corrosion resistance to the sintered body to be produced. By using a metal powder containing Cr, the corrosion resistance is increased, and a sintered body having good corrosion resistance can be obtained.

The Cr concentration A in the metal powder is 15.00% by mass or more and 17.50% by mass or less, preferably 15.20% by mass or more and 16.90% by mass or less, and more preferably 15.50% by mass or more and 16.70% by mass or less. If the Cr concentration A is below the lower limit, depending on the overall composition, the corrosion resistance of the sintered body to be manufactured may be insufficient. On the other hand, if the Cr concentration A is above the upper limit, depending on the overall composition, the sinterability may decrease, making it difficult to increase the density of the sintered body, and the corrosion resistance and mechanical properties of the sintered body may decrease.
The mechanical properties of the sintered body refer to properties such as mechanical strength and hardness.

1.2 Si
Silicon (Si) is an element that mainly imparts corrosion resistance and high mechanical properties to the sintered body to be produced. By using a metal powder containing Si, the corrosion resistance and mechanical properties are improved, and a sintered body having good corrosion resistance can be obtained.

The Si concentration B in the metal powder is 0.30% by mass or more and 1.00% by mass or less, preferably 0.35% by mass or more and 0.95% by mass or less, and more preferably 0.40% by mass or more and 0.90% by mass or less. If the Si concentration B is below the lower limit, the corrosion resistance, surface properties, and mechanical properties of the sintered body produced may be reduced depending on the overall composition. On the other hand, if the Si concentration B is above the upper limit, the composition balance may be easily lost depending on the overall composition, and the corrosion resistance, surface properties, and mechanical properties of the sintered body produced may be reduced.
The surface properties of the sintered body refer to properties such as mirror finish and smoothness.

1.3 Nb
Nb (niobium) is an element that causes precipitates to form in the sintered body to be produced, thereby improving the mechanical properties of the sintered body.
The Nb concentration C in the metal powder is 0.15% by mass or more and 0.45% by mass or less, preferably 0.20% by mass or more and 0.40% by mass or less, and more preferably 0.25% by mass or more and 0.35% by mass or less. If the Nb concentration C is below the lower limit, the precipitation of precipitates in the sintered body is restricted, and the mechanical properties of the sintered body may not be sufficiently improved. On the other hand, if the Nb concentration C exceeds the upper limit, the precipitates are excessively precipitated, the density of the sintered body decreases, and the mechanical properties of the sintered body are deteriorated.

1.4 Ni
Ni (nickel) is an element that mainly imparts corrosion resistance and heat resistance to the sintered body to be produced. By using a metal powder containing Ni, the corrosion resistance and heat resistance are increased, and a sintered body having good corrosion resistance and surface properties can be obtained.

The Ni concentration D in the metal powder is 3.00% by mass or more and 5.00% by mass or less, preferably 3.50% by mass or more and 4.70% by mass or less, and more preferably 3.80% by mass or more and 4.50% by mass or less. If the Ni concentration D is below the lower limit, depending on the overall composition, the corrosion resistance and surface properties of the sintered body to be manufactured may not be sufficiently improved. On the other hand, if the Ni concentration D is above the upper limit, depending on the overall composition, the balance of the composition may be easily lost, and the corrosion resistance and surface properties of the sintered body to be manufactured may be reduced.

1.5 Mn
Like Si, Mn (manganese) is an element that imparts corrosion resistance and high mechanical properties to the sintered body to be manufactured. By using a metal powder containing Mn, the corrosion resistance and mechanical properties are improved, and a sintered body having good corrosion resistance and mechanical properties can be obtained.

The Mn concentration E in the metal powder is not particularly limited, but is preferably 0.05% by mass to 1.00% by mass, more preferably 0.07% by mass to 0.50% by mass, and even more preferably 0.10% by mass to 0.40% by mass. If the Mn concentration E is below the lower limit, depending on the overall composition, the corrosion resistance, surface properties, and mechanical properties of the sintered body produced may not be sufficiently improved, while if the Mn concentration E exceeds the upper limit, the corrosion resistance, surface properties, and mechanical properties may be reduced.

1.6 Cu
Cu (copper) is an element that causes intermetallic compounds to precipitate in the sintered body to be produced, thereby improving the mechanical properties of the sintered body.
The Cu concentration F in the metal powder is 3.00% by mass or more and 5.00% by mass or less, preferably 3.10% by mass or more and 4.50% by mass or less, and more preferably 3.20% by mass or more and 4.20% by mass or less. If the Cu concentration F is below the lower limit, the precipitation of intermetallic compounds in the sintered body is restricted, and the mechanical properties of the sintered body may not be sufficiently improved. On the other hand, if the Cu concentration F exceeds the upper limit, the intermetallic compounds are excessively precipitated, the density of the sintered body decreases, and the mechanical properties of the sintered body are deteriorated.

1.7 Value of δ In the precipitation hardening stainless steel powder according to this embodiment, the value of δ defined by the following formula (1) is 10.0 mass % or more and 14.0 mass % or less.
δ=3(A+1.5B+0.5C)-2.8(D+0.5E+0.5F)-19.8... (1)

The value of δ defined in formula (1) can suppress the sinterability of the precipitation hardening stainless steel powder without impairing the mechanical properties of the sintered body produced using the precipitation hardening stainless steel powder. Specifically, the first term on the right side of formula (1) is a term related mainly to the elements that form ferrite, and the second term is a term related mainly to the elements that form austenite. Ferrite has a faster diffusion rate during sintering than austenite, and therefore contributes to increasing the sinterability of the precipitation hardening stainless steel powder.

In light of this, in this embodiment, the ratio of the concentration of elements that form ferrite to the concentration of elements that form austenite is optimized based on formula (1), thereby suppressing the sinterability of the resulting sintered body while maintaining the excellent mechanical strength derived from precipitation hardened stainless steel. More specifically, by setting the value of δ defined in formula (1) within the above range, it is possible to suppress the sinterability of the precipitation hardened stainless steel powder while maintaining the mechanical strength of the sintered body, and to slow the diffusion rate compared to conventional methods. This makes it possible to further increase the temperature at which the sintering of the metal powder begins when the compact is subjected to a sintering process. As a result, it is possible to more reliably remove the organic binder remaining in the compact before the metal powder begins to sinter.

Note that removal of the organic binder refers to, for example, the volatilization of the organic binder or its decomposition products, or the reaction of carbon atoms contained in the organic binder with oxygen atoms contained in the metal powder or oxygen atoms adsorbed to the metal powder, and the volatilization of the reaction products.

Here, the organic binder contains carbon atoms because it is mainly made of an organic compound. If the organic binder in the compact cannot be sufficiently removed, more carbon atoms than before will remain in the sintered body, which may reduce the mechanical strength of the sintered body. In contrast, in this embodiment, the sinterability of the precipitation hardening stainless steel powder is suppressed, thereby making it possible to increase the efficiency of removing the organic binder in the sintering process. This makes it possible to suppress the carbon atom concentration in the sintered body, making it possible to produce a sintered body with high mechanical strength.

The value of δ is 10.0 mass% or more and 14.0 mass% or less, preferably 10.5 mass% or more and 13.5 mass% or less, and more preferably 11.0 mass% or more and 13.0 mass% or less. If the value of δ is below the lower limit, the concentration of elements that form austenite increases. In this case, the sinterability of the precipitation hardened stainless steel powder decreases, but the sinterability tends to become too low, making it difficult to increase the density of the sintered body. This leads to a decrease in the mechanical strength of the resulting sintered body. On the other hand, if the value of δ exceeds the upper limit, the concentration of elements that form ferrite increases. In this case, the sinterability of the precipitation hardened stainless steel powder becomes too high, and the carbon atom concentration in the resulting sintered body increases. This leads to a decrease in the mechanical strength of the sintered body.

1.8 Fe
Among the elements contained in the precipitation hardening stainless steel powder according to the embodiment, Fe (iron) is the element with the highest content, i.e., the main component, and has a large effect on the properties of the sintered body produced. The Fe content is not particularly limited, but is preferably 50 mass% or more, and more preferably 60 mass% or more.

1.9 Other Elements The precipitation hardening stainless steel powder according to the embodiment may contain at least one of C, Mo, W, N, S and P, in addition to the elements described above, as necessary.

C (carbon) is an element that causes solid solution hardening as an interstitial element in the manufactured sintered body, or causes precipitation hardening by precipitates containing C or other elements. By using a metal powder containing C, a sintered body having high mechanical properties can be obtained. On the other hand, if the concentration of C, i.e., the carbon atom concentration, is too high, the mechanical properties of the sintered body, such as hardness, are reduced.
The C concentration in the metal powder is set to 0.07% by mass or less, preferably 0.01% by mass or more and 0.05% by mass or less. If the C concentration exceeds the upper limit, depending on the overall composition, the composition balance is likely to be lost, and the mechanical properties of the sintered body to be produced may be deteriorated.

Mo (molybdenum) is an element that enhances the corrosion resistance of the produced sintered body.
The Mo concentration in the metal powder is not particularly limited, but is preferably 1.00 mass% or less, and more preferably 0.01 mass% to 0.50 mass%. By setting the Mo concentration within the above range, the corrosion resistance of the sintered body can be further enhanced without causing a significant decrease in the density of the sintered body to be produced.

W (tungsten) is an element that enhances the heat resistance of the sintered body to be produced.
The W concentration in the metal powder is not particularly limited, but is preferably 1.00 mass% or less, and more preferably 0.01 mass% to 0.50 mass%. By setting the W concentration within the above range, the heat resistance of the sintered body can be further enhanced without causing a significant decrease in the density of the sintered body to be produced.

N (nitrogen) is an element that enhances mechanical properties such as the yield strength of the produced sintered body.
The concentration of N in the metal powder is not particularly limited, but is preferably 1.00 mass% or less, more preferably 0.001 mass% to 0.50 mass% or less, and even more preferably 0.05 mass% to 0.30 mass% or less. By setting the concentration of N within the above range, it is possible to further improve the mechanical properties such as the yield strength of the sintered body without causing a significant decrease in the density of the sintered body produced.

To manufacture metal powder with added N, for example, a method using a nitrided raw material, a method of introducing nitrogen gas into molten metal, a method of subjecting the manufactured metal powder to a nitriding treatment, etc. can be used.

S (sulfur) is an element that enhances the machinability of the produced sintered body.
The concentration of S in the metal powder is not particularly limited, but is preferably 0.50 mass% or less, and more preferably 0.001 mass% to 0.30 mass% or less. By setting the concentration of S within the above range, the machinability of the sintered body to be produced can be further improved without causing a significant decrease in the density of the sintered body to be produced.

P (phosphorus) is an element that acts as an interstitial element to cause solid solution hardening in the sintered body being manufactured, and also causes precipitation hardening through precipitates formed by combining with other elements. By using metal powder containing P, sintered bodies with high mechanical properties can be obtained.

The P concentration in the metal powder is 0.50% by mass or less, preferably 0.001% by mass to 0.35% by mass or less, and more preferably 0.005% by mass to 0.30% by mass or less. If the P concentration is below the lower limit, depending on the overall composition, the mechanical properties of the sintered body may not be sufficiently improved even if P is added. On the other hand, if the P concentration exceeds the upper limit, depending on the overall composition, the composition may become unbalanced, and the mechanical properties of the sintered body produced may be reduced.

O (oxygen) may be intentionally added or unavoidably contained, but its concentration is preferably 0.01% by mass or more and 0.70% by mass or less, and more preferably 0.15% by mass or more and 0.60% by mass or less. By keeping the O concentration in the metal powder within this range, silicon oxide precipitates on the particle surfaces of the metal powder, so that oxidation of elements such as Mn and Cr can be suppressed. As a result, the corrosion resistance and surface properties of the sintered body finally produced can be improved.
If the O content falls below the lower limit, the amount of silicon oxide precipitated is reduced, which may lead to the oxidation of elements such as Mn and Cr. In this case, the corrosion resistance, surface properties, and mechanical properties of the sintered body produced may be degraded. On the other hand, if the O content exceeds the upper limit, in addition to silicon oxide, oxides of Mn and Cr are also generated at the time of producing the metal powder. For this reason, it becomes difficult to increase the density of the sintered body produced, and this may lead to a decrease in the corrosion resistance, surface properties, and mechanical properties.

The concentration of O is more preferably 0.20% by mass or more and 0.55% by mass or less, and particularly preferably 0.33% by mass or more and 0.53% by mass or less. By keeping the concentration of O in the metal powder within this range, in addition to the above effects, oxygen atoms in the metal powder can react with carbon atoms derived from the organic binder. For example, when oxygen atoms in the metal powder exist as silicon oxide, oxygen atoms and carbon atoms can be removed from the sintered body by the reaction represented by the following formula (2).
SiO ₂ +2C→Si+2CO↑ ...(2)
By such a reaction, the carbon atoms derived from the organic binder can be consumed and removed using oxygen atoms. Therefore, by including a predetermined amount of oxygen atoms, the concentration of carbon atoms derived from the organic binder remaining in the sintered body can be suppressed.

If the O concentration falls below the lower limit, the carbon atoms in the sintered body may not be consumed sufficiently. On the other hand, if the O concentration exceeds the upper limit, the composition may become unbalanced, and the mechanical strength and corrosion resistance of the sintered body may decrease.

In addition to the elements mentioned above, the precipitation hardening stainless steel powder may contain H, Be, B, Al, Co, As, Sn, Se, Zr, Y, Ti, Hf, Ta, Te, Pb, etc. to enhance the properties of the sintered body. In this case, the concentrations of these elements are not particularly limited, but should be such that they do not impair the properties of the sintered body described above, and are preferably less than 0.1 mass% each, and preferably less than 0.2 mass% in total. Note that these elements may be unavoidably included.

Furthermore, the precipitation hardening stainless steel powder may contain unavoidable impurities. Examples of impurities include all elements other than those mentioned above. The concentration of each of these impurities may be less than the respective concentrations of Fe, Cr, Si, Nb, Ni, Mn, and Cu. In particular, the concentration of each of these impurities is preferably less than 0.03 mass%, and the total concentration of the impurities is preferably less than 0.30 mass%. Note that these impurities may be intentionally added, as long as their concentrations are within the above ranges, and the effects described above are not inhibited.

The tap density of the precipitation hardening stainless steel powder is preferably 3.5 g/cm3 or ^more and 5.5 g/cm3 ^or less, and more preferably 4.0 g/cm3 or ^more and 5.0 g/cm3 or ^less . Such a precipitation hardening stainless steel powder provides particularly high interparticle packing when a compact is obtained. As a result, a particularly dense sintered body can be obtained in the end.

The specific surface area of the precipitation hardening stainless steel powder is preferably 0.10 ^m2 /g or more and 0.70 ^m2 /g or less, more preferably 0.15 ^m2 /g or more and 0.50 ^m2 /g or less. Such a precipitation hardening stainless steel powder optimizes the surface activity (surface energy) and provides suitable sinterability. This makes it possible to obtain a sufficient sintering rate while suppressing the organic binder, its decomposition products, and the reaction products of carbon atoms from remaining in the sintered body. As a result, a dense sintered body can be obtained while reducing the carbon atom concentration.

1.10 Analysis Method The composition ratio of the precipitation hardening stainless steel powder according to the embodiment can be determined by, for example, iron and steel-atomic absorption spectrometry as specified in JIS G 1257:2000, iron and steel-ICP optical emission spectrometry as specified in JIS G 1258:2007, iron and steel-spark discharge optical emission spectrometry as specified in JIS G 1253:2002, iron and steel-fluorescent X-ray analysis as specified in JIS G 1256:1997, and gravimetric/titration/absorption spectrometry as specified in JIS G 1211 to G 1237. Specifically, for example, a spark discharge optical emission spectrometer manufactured by SPECTRO, Inc., a solid-state optical emission spectrometer, model: SPECTROLAB, type: LAVMB08A, and an ICP device manufactured by Rigaku Corporation, CIROS120 type, can be mentioned.

In addition, JIS G 1211 to G 1237 are as follows.
JIS G 1211:2011 Iron and steel-Determination of carbon JIS G 1212:1997 Iron and steel-Determination of silicon JIS G 1213:2001 Iron and steel-Determination of manganese JIS G 1214:1998 Iron and steel-Determination of phosphorus JIS G 1215:2010 Iron and steel-Determination of sulfur JIS G 1216:1997 Iron and steel-Determination of nickel JIS G 1217:2005 Iron and steel-Determination of chromium JIS G 1218:1999 Iron and steel-Determination of molybdenum JIS G 1219:1997 Iron and steel-Determination of copper JIS G 1220:1994 Iron and steel-Determination of tungsten JIS G JIS G 1221:1998 Iron and steel-Determination of vanadium JIS G 1222:1999 Iron and steel-Determination of cobalt JIS G 1223:1997 Iron and steel-Determination of titanium JIS G 1224:2001 Iron and steel-Determination of aluminum JIS G 1225:2006 Iron and steel-Determination of arsenic JIS G 1226:1994 Iron and steel-Determination of tin JIS G 1227:1999 Iron and steel-Determination of boron JIS G 1228:2006 Iron and steel-Determination of nitrogen JIS G 1229:1994 Steel-Determination of lead JIS G 1232:1980 Steel-Determination of zirconium JIS G 1233:1994 Steel-Determination of selenium JIS G 1234:1981 Determination of tellurium in steel JIS G 1235:1981 Determination of antimony in iron and steel JIS G 1236:1992 Determination of tantalum in steel JIS G 1237:1997 Determination of niobium in iron and steel

In addition, when specifying C (carbon) and S (sulfur), the oxygen flow combustion high-frequency induction heating furnace combustion-infrared absorption method specified in JIS G 1211: 2011 is also used. A specific example of an analytical device is the LECO carbon/sulfur analyzer, CS-200.
Furthermore, when specifying N (nitrogen) and O (oxygen), the nitrogen determination method for iron and steel specified in JIS G 1228: 2006 and the oxygen determination method for metallic materials specified in JIS Z 2613: 2006 are particularly used. Specific examples of the analyzer include the oxygen/nitrogen analyzer TC-300/EF-300 manufactured by LECO Corporation.

In addition, a sintered body manufactured using the precipitation hardening stainless steel powder according to the embodiment can be subjected to various heat treatments to precipitate a martensite crystal structure. The martensite crystal structure imparts high hardness to the sintered body. Whether or not the sintered body has a martensite crystal structure can be determined, for example, by X-ray diffraction.

The average particle size of the precipitation hardening stainless steel powder is preferably 0.50 μm to 50.00 μm, more preferably 1.00 μm to 30.00 μm, and even more preferably 2.00 μm to 10.00 μm. By using a precipitation hardening stainless steel powder with such a particle size, the number of voids remaining in the sintered body is extremely reduced, making it possible to produce a sintered body that is high in density and has excellent mechanical properties.
If the average particle size of the precipitation hardening stainless steel powder is below the lower limit, the moldability may decrease when forming a shape that is difficult to form, and the sintered density may decrease. On the other hand, if the average particle size of the precipitation hardening stainless steel powder is above the upper limit, the gaps between the particles may become large during forming, and the sintered density may decrease.
The average particle size of the precipitation hardening stainless steel powder is determined as the particle size at which the cumulative amount from the small diameter side is 50% in a cumulative particle size distribution on a mass basis obtained by a laser diffraction method.

The maximum particle size of the precipitation hardening stainless steel powder is not particularly limited as long as the average particle size is within the above range, but is preferably 200 μm or less, and more preferably 150 μm or less. By controlling the maximum particle size of the precipitation hardening stainless steel powder within the above range, the particle size distribution of the precipitation hardening stainless steel powder can be narrowed further, and the sintered body can be made even denser.
The maximum particle size mentioned above refers to the particle size at which the cumulative amount from the small diameter side is 99.9% in the cumulative particle size distribution on a mass basis obtained by a laser diffraction method.

When the minor axis of the particles of the precipitation hardening stainless steel powder is S [μm] and the major axis is L [μm], the average aspect ratio defined by S/L is preferably about 0.4 to 1, more preferably about 0.7 to 1. Precipitation hardening stainless steel powder with such an aspect ratio has a shape that is relatively close to a sphere, which increases the filling rate when molded. As a result, the sintered body can be made even denser.

The long diameter is the maximum length that the particle can have in a projected image, and the short diameter is the maximum length that the particle can have in a direction perpendicular to the long diameter. The average aspect ratio is the average aspect ratio measured for 100 or more particles.

2. Method for Producing a Precipitation Hardening Stainless Steel Sintered Body Next, a method for producing a precipitation hardening stainless steel sintered body according to an embodiment will be described.
FIG. 1 is a process diagram showing a method for producing a precipitation hardening stainless steel sintered body according to an embodiment.
The method for producing a precipitation hardened stainless steel sintered body shown in Fig. 1 includes a composition preparation step S1 for preparing a composition for producing the sintered body, a molding step S2 for molding the composition, a degreasing step S3 for degreasing the molded body, and a firing step S4 for firing the degreased body. Each step will be described below in order.

2.1 Composition preparation step S1
First, the precipitation hardening stainless steel powder and the organic binder are kneaded with a kneader to obtain a kneaded product, i.e., a compound according to the embodiment. The kneaded product is the above-mentioned precipitation hardening stainless steel powder, the organic binder, According to such a kneaded product, although an organic binder is used, it is possible to produce a sintered body having high mechanical strength.

Precipitation hardening stainless steel powder is produced by various powdering methods, such as atomization methods such as water atomization, gas atomization, and high-speed rotating water flow atomization, reduction methods, carbonyl methods, and pulverization methods.

Of these, the precipitation hardening stainless steel powder is preferably produced by the atomization method, and more preferably by the water atomization method or the high-speed rotating water flow atomization method. The atomization method is a method of producing metal powder by colliding molten metal with a liquid or gas sprayed at high speed, pulverizing it and cooling it. By producing the precipitation hardening stainless steel powder by such an atomization method, extremely fine powder can be produced efficiently. In addition, the particle shape of the obtained powder becomes close to spherical due to the action of surface tension. Therefore, when molded, a product with a high filling rate can be obtained. In other words, a powder that can be used to produce a high-density sintered body can be obtained.

When the water atomization method is used as the atomization method, the pressure of the water sprayed toward the molten metal is not particularly limited, but is preferably about 75 MPa or more and 120 MPa or less, and more preferably about 90 MPa or more and 120 MPa or less.
The temperature of the atomized water is not particularly limited, but is preferably about 1° C. or higher and 20° C. or lower.
Furthermore, the atomized water is often sprayed in a cone shape having an apex on the falling path of the molten metal and an outer diameter that gradually decreases downward. In this case, the apex angle θ of the cone formed by the atomized water is preferably about 10° to 40°, and more preferably about 15° to 35°. This makes it possible to reliably produce the precipitation hardening stainless steel powder having the composition described above.

Furthermore, water atomization, particularly high-speed rotating water jet atomization, allows the molten metal to be cooled particularly quickly, which makes it possible to obtain high-quality powder over a wide range of alloy compositions.
In the atomization method, the cooling rate for cooling the molten metal is preferably 1×10 ⁴ °C/s or more, and more preferably 1×10 ⁵ °C/s or more. Such rapid cooling makes it possible to obtain a homogeneous precipitation hardening stainless steel powder. As a result, a high-quality sintered body can be obtained.

The precipitation hardening stainless steel powder thus obtained may be classified as necessary. Examples of classification methods include dry classification such as sieving classification, inertial classification, and centrifugal classification, and wet classification such as sedimentation classification.

As the organic binder, a resin that can be decomposed in a short time during degreasing or baking is used. Examples of such resins include polyolefins such as polyethylene, polypropylene, and ethylene-vinyl acetate copolymers; acrylic resins such as polymethyl methacrylate and polybutyl methacrylate; styrene resins such as polystyrene; polyesters such as polyvinyl chloride, polyvinylidene chloride, polyamide, polyethylene terephthalate, and polybutylene terephthalate; polyethers, polyvinyl alcohol, polyvinylpyrrolidone, or copolymers thereof; various waxes, paraffin, higher fatty acids, higher alcohols, higher fatty acid esters, and higher fatty acid amides; and one or more of these can be used in combination.

The mixing ratio of the organic binder is preferably about 2% by mass or more and 20% by mass or less of the entire kneaded product, and more preferably about 5% by mass or more and 15% by mass or less. By having the mixing ratio of the organic binder within the above range, a molded body can be formed with good moldability, and the density can be increased, making the shape stability of the molded body particularly excellent. This also makes it possible to optimize the difference in size between the molded body and the degreased body, the so-called shrinkage rate, and prevent a decrease in the dimensional accuracy of the finally obtained sintered body. In other words, a sintered body with high density and dimensional accuracy can be obtained.

If necessary, a plasticizer may be added to the kneaded material. Examples of the plasticizer include phthalic acid esters, adipic acid esters, trimellitic acid esters, and sebacic acid esters, and one or more of these may be mixed and used.
Furthermore, in addition to the precipitation hardening stainless steel powder, organic binder, and plasticizer, various additives such as lubricants, antioxidants, degreasing accelerators, surfactants, other metal powders, ceramic powders, etc. may be added to the kneaded product as necessary.

The kneading conditions vary depending on various conditions such as the alloy composition and particle size of the precipitation hardening stainless steel powder used, the composition of the organic binder, and the amounts of these blended, but an example can be a kneading temperature of about 50° C. or higher and 200° C. or lower, and a kneading time of about 15 minutes or higher and 210 minutes or lower.
The kneaded product is pelletized as necessary. The particle size of the pellets is, for example, about 1 mm or more and 15 mm or less.

Depending on the molding method described below, the granulated powder according to the embodiment may be used instead of the kneaded material. These kneaded materials and granulated powders are examples of compositions that are subjected to the molding process described below.

Such granulated powder is produced by subjecting precipitation hardened stainless steel powder to a granulation process, resulting in multiple metal particles being bound together by an organic binder. In other words, the granulated powder is a composition containing the above-mentioned precipitation hardened stainless steel powder and an organic binder. With such granulated powder, it is possible to produce a sintered body with high mechanical strength, even though an organic binder is used.

Organic binders used in the production of granulated powder include, for example, the organic binders mentioned above.

The mixing ratio of the organic binder is preferably about 0.2% by mass or more and 10% by mass or less of the total granulated powder, and more preferably about 0.3% by mass or more and 5.0% by mass or less. By having the mixing ratio of the organic binder within the above range, the granulated powder can be efficiently formed while suppressing the granulation of extremely large particles and the remaining of a large amount of ungranulated metal particles. In addition, since the moldability is improved, the shape stability of the molded body can be particularly excellent. In addition, by setting the mixing ratio of the organic binder within the above range, the difference in size between the molded body and the degreased body, that is, the shrinkage rate, can be optimized, and the dimensional accuracy of the finally obtained sintered body can be prevented from decreasing.

In addition to the precipitation hardening stainless steel powder, organic binder, and plasticizer, the granulated powder may also contain various additives such as lubricants, antioxidants, degreasing agents, and surfactants, as well as other metal powders and ceramic powders.

Examples of the granulation process include spray drying, tumbling granulation, fluidized bed granulation, and tumbling fluidized bed granulation.
In the granulation process, a solvent that dissolves the binder is used as necessary. Examples of such solvents include inorganic solvents such as water and carbon tetrachloride, and organic solvents such as ketone solvents, alcohol solvents, ether solvents, cellosolve solvents, aliphatic hydrocarbon solvents, aromatic hydrocarbon solvents, aromatic heterocyclic compound solvents, amide solvents, halogenated compound solvents, ester solvents, amine solvents, nitrile solvents, nitro solvents, and aldehyde solvents, and one or a mixture of two or more selected from these solvents is used.

The average particle size of the granulated powder is not particularly limited, but is preferably about 10 μm to 200 μm, more preferably about 20 μm to 100 μm, and even more preferably about 25 μm to 60 μm. Granulated powder with such a particle size has good flowability and can more faithfully reflect the shape of the mold.
The average particle size is determined as the particle size at which the cumulative amount from the small diameter side becomes 50% in a cumulative particle size distribution on a mass basis obtained by a laser diffraction method.

2.2 Molding process S2
Next, the kneaded mixture or granulated powder is molded to produce a molded body having the same shape as the desired sintered body.
Examples of the molding method include powder compaction, metal powder injection molding, and extrusion molding.

Of these, the molding conditions for the powder compaction method vary depending on various conditions such as the composition and particle size of the precipitation hardening stainless steel powder used, the composition of the organic binder, and the amounts of these mixed, but it is preferable for the molding pressure to be approximately 200 MPa or more and 1000 MPa or less.

In addition, the molding conditions for metal powder injection molding vary depending on various conditions, but it is preferable that the material temperature is approximately 80°C or higher and 210°C or lower, and the injection pressure is approximately 50 MPa or higher and 500 MPa or lower.

In the case of extrusion molding, the molding conditions vary depending on various conditions, but it is preferable that the material temperature is about 80° C. or more and 210° C. or less, and the extrusion pressure is about 50 MPa or more and 500 MPa or less.
The shape and dimensions of the green body to be produced are determined taking into account the shrinkage of the green body during the debinding and firing steps described below.

2.3 Degreasing step S3
Next, the obtained green body is subjected to a degreasing treatment to obtain a degreased body. Specifically, the degreasing treatment is performed by decomposing and removing the organic binder.
Examples of the degreasing treatment include a method of heating the molded body and a method of exposing the molded body to a gas that decomposes the organic binder.

When using the method of heating the molded body, the heating conditions for the molded body vary slightly depending on the composition and amount of the organic binder, but are preferably at a temperature of 100°C to 750°C x 0.1 to 20 hours, and more preferably at a temperature of 150°C to 600°C x 0.5 to 15 hours. This allows the molded body to be degreased as necessary and sufficiently without sintering it. As a result, it is possible to prevent a large amount of organic binder components from remaining inside the degreased body.

The atmosphere in which the molded body is heated is not particularly limited, and examples include a reducing gas atmosphere such as hydrogen, an inert gas atmosphere such as nitrogen or argon, an oxidizing gas atmosphere such as air, or a reduced pressure atmosphere obtained by reducing the pressure of these atmospheres.

On the other hand, an example of a method for exposing a molded body to a gas that decomposes the organic binder is the acid degreasing method. The acid degreasing method is a method for degreasing a molded body by heating the body in an acid-containing atmosphere, utilizing the catalytic action of the acid. With the acid degreasing method, the organic binder can be decomposed in a short time even at low temperatures, so even large molded bodies can be efficiently degreased.

An acid-containing atmosphere refers to an atmosphere that contains an acid capable of decomposing an organic binder. Examples of such acids include nitric acid, oxalic acid, ozone, etc., and one or more of these can be used in combination. A mixed gas in which these acids are mixed with other gases may also be used. An example of a mixed gas is fuming nitric acid. The atmospheric pressure may be atmospheric pressure, reduced pressure, or pressurized.

The heating conditions for the molded body vary slightly depending on the composition and amount of the organic binder and the type of acid-containing atmosphere, but are preferably at a temperature of 100°C to 750°C for 0.1 to 20 hours, and more preferably at a temperature of 150°C to 600°C for 0.5 to 15 hours. This allows the molded body to be degreased in a short time even at a relatively low temperature. It also prevents the molded body from sintering or oxidizing.

Incidentally, such a debinding step may be carried out in a plurality of separate steps each having different debinding conditions, so that the binder in the green body can be decomposed and removed more quickly and without remaining in the green body.
If necessary, the degreased body may be subjected to machining such as cutting, grinding, and cutting. Since the degreased body has a relatively low hardness and is relatively plastic, it can be easily machined while preventing the shape of the degreased body from being distorted. By such machining, a sintered body with high dimensional accuracy can be easily obtained.

2.4 Firing step S4
Next, the obtained degreased body is subjected to a sintering treatment. The sintering treatment causes surface diffusion at the interfaces between the particles of the precipitation hardened stainless steel powder, leading to sintering. As a result, a sintered body is obtained.

The firing temperature varies depending on the composition and particle size of the precipitation hardening stainless steel powder used to manufacture the compact and the degreased body, but is, for example, about 980° C. to 1330° C., and preferably about 1050° C. to 1260° C.
The firing time is set to 0.2 hours or more and 7 hours or less, and preferably 1 hour or more and 6 hours or less.

In the firing step, the firing temperature or the firing atmosphere, which will be described later, may be changed midway.
By setting the sintering conditions within these ranges, it is possible to sinter the entire degreased body sufficiently while preventing oversintering, which would otherwise cause the crystal structure to become enlarged, and as a result, it is possible to obtain a sintered body that is high in density and has excellent mechanical properties.

The sintered body thus produced may be subjected to additional treatments as necessary. Examples of additional treatments include solution treatment, age hardening, double aging, sub-zero treatment, tempering, hot working, and cold working, and one or more of these may be used in combination.

Specific examples of the above-mentioned additional treatments include a solution treatment in which the material is cooled from a temperature of 1000°C to 1250°C for a period of 30 to 120 minutes, followed by an age hardening treatment in which the material is cooled from a temperature of 600°C to 800°C for a period of 6 to 48 hours.

3. Precipitation hardening stainless steel sintered body As described above, the precipitation hardening stainless steel sintered body according to this embodiment is a sintered body made of precipitation hardening stainless steel containing Cr, Si, Nb, Ni, Mn and Cu. In this sintered body, Cr is contained at a concentration A in the range of 15.00 mass% to 17.50 mass%, Si is contained at a concentration B in the range of 0.30 mass% to 1.00 mass%, Nb is contained at a concentration C in the range of 0.15 mass% to 0.45 mass%, Ni is contained at a concentration D in the range of 3.00 mass% to 5.00 mass%, Mn is contained at a concentration E in the range of 0.05 mass% to 1.00 mass%, and Cu is contained at a concentration F in the range of 3.00 mass% to 5.00 mass%. In addition, in this sintered body, the value of δ defined by the following formula (1) is 10.0 mass% to 14.0 mass%.
δ=3(A+1.5B+0.5C)-2.8(D+0.5E+0.5F)-19.8... (1)
According to such a precipitation hardening stainless steel sintered body, an increase in the carbon atom concentration is suppressed, and therefore a sintered body having high mechanical strength derived from the precipitation hardening stainless steel can be obtained. In particular, even when the sintered body is small or has a complex shape, the residual carbon atoms derived from the organic binder are suppressed, and a high-quality sintered body can be obtained.

Precipitation hardening stainless steel sintered bodies can be used as materials for constituting all or part of, for example, automobile parts, bicycle parts, railroad vehicle parts, ship parts, aircraft parts, and space transport vehicle parts; electronic device parts, such as personal computer parts, mobile phone terminal parts, tablet terminal parts, and wearable terminal parts; electrical device parts, such as refrigerators, washing machines, and air conditioners; machine parts, such as machine tools and semiconductor manufacturing equipment; plant parts, such as nuclear power plants, thermal power plants, hydroelectric power plants, refineries, and chemical complexes; watch parts, and decorative items, such as metal tableware, jewelry, and eyeglass frames.

As described above, the method for producing a precipitation hardening stainless steel sintered body according to this embodiment includes a molding step of molding a compound or granulated powder containing precipitation hardening stainless steel powder to obtain a molded body, and a sintering step of sintering the molded body to obtain a sintered body. In such a manufacturing method, the carbon atom concentration in the sintered body is preferably smaller than the carbon atom concentration in the precipitation hardening stainless steel powder. This is because the carbon atom concentration in the sintered body is reduced by the reaction between carbon atoms and oxygen atoms as described above. By reducing the carbon atom concentration in the sintered body in this way, the carbon atom concentration in the sintered body can be kept within the above-mentioned range even when a precipitation hardening stainless steel powder with a high carbon atom concentration is used. This makes it possible to efficiently produce a sintered body with high mechanical strength.

When the carbon atom concentration in the precipitation hardened stainless steel powder is the first concentration c1 and the carbon atom concentration in the sintered body is the second concentration c2, (c1-c2)/c1 is preferably 70 mass% or less, and more preferably 50 mass% or less. This ensures that the first concentration c1 can be reduced, increasing the probability that the second concentration c2 can be kept within the aforementioned range. As a result, it is possible to more reliably manufacture a sintered body that has high mechanical strength, hardness, and corrosion resistance derived from precipitation hardened stainless steel.

The precipitation hardening stainless steel powder, compound, granulated powder, precipitation hardening stainless steel sintered body, and the manufacturing method thereof according to the present invention have been described above based on preferred embodiments, but the present invention is not limited to these. For example, any additive may be added to the compound and granulated powder.
The method for producing a precipitation hardened stainless steel sintered body of the present invention may be obtained by adding any step for any purpose to the above-described embodiment.

Next, an embodiment of the present invention will be described.
4. Production of sintered body (Sample No. 1)
[1] First, a precipitation hardening stainless steel powder having the composition shown in Table 1 was prepared by water atomization.
The compositions of the metal powders shown in Table 1 were identified and quantified using inductively coupled plasma emission spectrometry and a Rigaku Corporation ICP apparatus CIROS120. C was identified and quantified using a LECO Corporation carbon/sulfur analyzer CS-200. O was identified and quantified using a LECO Corporation oxygen/nitrogen analyzer TC-300/EF-300.

[2] Next, the metal powder and the organic binder were weighed and mixed in a mass ratio of 89:11 to obtain a mixed raw material. Note that, for the organic binder, a resin obtained by mixing a polyacetal resin containing 2.5 mass% butanediol and polyethylene in a mass ratio of 50:6 was used.
[3] Next, the mixed raw materials were kneaded in a kneader to obtain a compound.
[4] Next, this compound was molded in an injection molding machine under the molding conditions shown below to produce a molded body.
<Molding conditions>
・Material temperature: 180℃
Injection pressure: 11 MPa (110 kgf/ ^cm2 )

[5] Next, the obtained molded body was subjected to a degreasing treatment under the degreasing conditions shown below to obtain a degreasing body.
<Degreasing conditions>
・Degreasing temperature: 400℃
Degreasing time: 1 hour (retention time at degreasing temperature)
Degreasing atmosphere: A mixed gas atmosphere of nitrogen and nitric acid, with the concentration of nitric acid being 2% by volume

[6] Next, the obtained degreased body was subjected to a sintering treatment under the sintering conditions shown below to obtain a sintered body. The shape of the sintered body was a cylinder with a diameter of 10 mm and a thickness of 5 mm.
<Firing conditions>
Firing temperature: 1300°C
Firing time: 3 hours (retention time at firing temperature)
Firing atmosphere: Argon atmosphere

[7] Next, the obtained sintered body was subjected to a solution treatment and an age hardening treatment in this order under the conditions shown below.
<Solution treatment conditions>
・Heating temperature: 1120℃
Heating time: 30 minutes Cooling method: Water cooling <Age hardening treatment conditions>
・Heating temperature: 700℃
・Heating time: 24 hours ・Cooling method: Water cooling

(Sample No. 2 to 13)
Except for changing the composition of the precipitation hardening stainless steel powder as shown in Table 1, sintered bodies were obtained in the same manner as in the case of sample No. 1. The powder of sample No. 5 was produced by gas atomization.
In Table 1, among the precipitation hardening stainless steel powders and sintered bodies of each sample number, those that correspond to the present invention are designated as "Examples", and those that do not correspond to the present invention are designated as "Comparative Examples".
Although each sintered body contained a small amount of impurities, the contents of these impurities are omitted in Table 1.

5. Evaluation of Precipitation Hardening Stainless Steel Powder and Precipitation Hardening Stainless Steel Sintered Body 5.1 Measurement of Average Powder Particle Size The average particle size was measured for the powder of each sample number shown in Table 1. The measurement results are shown in Table 1.

5.2 Measurement of tap density of powder The tap density was measured for each sample No. shown in Table 1. A powder property evaluation device, Powder Tester (registered trademark) PT-X, manufactured by Hosokawa Micron Corporation, was used to measure the tap density. The number of taps was 125. The measurement results are shown in Table 1. In addition, since the powder of sample No. 5 has a large particle size, the tap density measurement was omitted.

5.3 Measurement of Specific Surface Area of Powder The specific surface area of each powder sample No. shown in Table 1 was measured. The specific surface area was measured using the BET method, and a BET specific surface area measuring device HM1201-010 manufactured by Mountec Co., Ltd. was used. The amount of the sample was 5 g. The measurement results are shown in Table 1. In addition, since the powder sample No. 5 has a large particle size, the measurement of the specific surface area was omitted.

5.4 Measurement of Carbon Atom Concentration in Sintered Body The carbon atom concentration was measured for the sintered body of each sample No. shown in Table 1. The measurement results are shown in Table 1.

5.5 Evaluation of mechanical strength of sintered body Test pieces as specified in ISO 2740:2009 were cut out from the sintered body of each sample No. shown in Table 1. The tensile strength of the test pieces was measured by the test method as specified in JIS Z 2241:2011.
Next, the tensile strength measured for the sintered body of Sample No. 10 was set to 1, and the relative values of the tensile strength measured for the sintered bodies of each Example and Comparative Example were calculated.
The calculated relative values were then evaluated according to the following evaluation criteria.

<Evaluation criteria for tensile strength>
A: The tensile strength is very high (relative value is greater than 1.1)
B: High tensile strength (relative value is greater than 1 and less than 1.1)
C: Low tensile strength (relative value greater than 0.9 and less than 1)
D: The tensile strength is very small (relative value is 0.9 or less)
The evaluation results are shown in Table 1.

5.6 Evaluation of Hardness of Sintered Body The Vickers hardness of each sintered body of sample No. shown in Table 1 was measured.
Next, the Vickers hardness measured for the sintered body of Sample No. 10 was set to 1, and the relative values of the Vickers hardness measured for the sintered bodies of each of the Examples and Comparative Examples were calculated.
The calculated relative values were then evaluated according to the following evaluation criteria.

<Hardness evaluation criteria>
A: Very high hardness (relative value exceeds 1.1)
B: High hardness (relative value is greater than 1 and less than 1.1)
C: Low hardness (relative value is greater than 0.9 and less than 1)
D: Very low hardness (relative value 0.9 or less)
The evaluation results are shown in Table 1.

5.7 Evaluation of relative density of sintered body The density of each sintered body of sample No. shown in Table 1 was measured by a method based on Archimedes' method. The relative density of the sintered body was calculated from the measured density and the true density of the soft magnetic powder.
Next, the calculated relative density was evaluated based on the following evaluation criteria.

<Relative density evaluation criteria>
A: The relative density was 98.0% or more. B: The relative density was less than 98.0%. The evaluation results are shown in Table 1.

5.8 Evaluation of Corrosion Resistance of Sintered Body The corrosion degree of each sintered body of sample No. shown in Table 1 was measured in accordance with the sulfuric acid corrosion test method for stainless steel specified in JIS G 0591: 2012. Note that boiled 5 mass% sulfuric acid was used as the sulfuric acid.
Next, the corrosion degree measured for the sintered body of each sample No. was calculated as a relative value when the corrosion degree (unit: g/ ^m2 /h) measured for the sintered body of sample No. 10 was set as 1. The calculated relative values were then evaluated in accordance with the following evaluation criteria.

<Corrosion resistance evaluation criteria>
A: The relative value of the corrosion degree of the sintered body is less than 0.75. B: The relative value of the corrosion degree of the sintered body is 0.75 or more and less than 1.00. C: The relative value of the corrosion degree of the sintered body is 1.00 or more and less than 1.25. D: The relative value of the corrosion degree of the sintered body is 1.25 or more. The above evaluation results are shown in Table 1.

As is apparent from Table 1, the sintered bodies of the examples had good mechanical strength, hardness and corrosion resistance.
In addition, in each example, the carbon atom concentration in the sintered body was lower than that in the powder, which suggests that in each example, the reaction products of carbon atoms were efficiently removed during the sintering process, resulting in improved mechanical properties and improved corrosion resistance.
In the above, a sintered body was obtained by using a molded body produced by injection molding using a compound containing precipitation hardening stainless steel powder. On the other hand, a sintered body was also obtained by using a molded body produced by pressure molding using a granulated powder containing precipitation hardening stainless steel powder. As a result, the same tendency as when a compound was used was observed.

S1...composition preparation process, S2...molding process, S3...degreasing process, S4...baking process

Claims (8)

Cr is contained at a concentration A in the range of 15.00 mass% or more and 17.50 mass% or less,
Si is contained at a concentration B in the range of 0.30 mass% or more and 1.00 mass% or less,
Nb is contained at a concentration C in the range of 0.15 mass% or more and 0.45 mass% or less,
Ni is contained at a concentration D in the range of 3.00 mass% or more and 5.00 mass% or less,
Mn is contained at a concentration E in the range of 0.05 mass% or more and 1.00 mass% or less,
Cu is contained at a concentration F in the range of 3.00 mass% or more and 5.00 mass% or less,
A precipitation hardening stainless steel powder characterized in that the value of δ defined by the following formula (1) is 10.0 mass % or more and 13.5 mass % or less.
δ=3(A+1.5B+0.5C)-2.8(D+0.5E+0.5F)-19.8・
...(1) 2. The precipitation hardening stainless steel powder according to claim 1, wherein O is contained at a concentration in the range of 0.01 mass % or more and 0.70 mass % or less. 3. The precipitation hardening stainless steel powder according to claim 2, wherein O is contained at a concentration in the range of 0.33 mass % or more and 0.53 mass % or less. 4. Any one of claims 1 to 3, wherein the average particle size is 0.50 μm or more and 50.00 μm or less.
Item 3. The precipitation hardening stainless steel powder according to item 1. A compound comprising the precipitation hardening stainless steel powder according to any one of claims 1 to 4 and an organic binder. A granulated powder comprising the precipitation hardening stainless steel powder according to any one of claims 1 to 4 and an organic binder. Cr is contained at a concentration A in the range of 15.00 mass% or more and 17.50 mass% or less,
Si is contained at a concentration B in the range of 0.30 mass% or more and 1.00 mass% or less,
Nb is contained at a concentration C in the range of 0.15 mass% or more and 0.45 mass% or less,
Ni is contained at a concentration D in the range of 3.00 mass% or more and 5.00 mass% or less,
Mn is contained at a concentration E in the range of 0.05 mass% or more and 1.00 mass% or less,
Cu is contained at a concentration F in the range of 3.00 mass% or more and 5.00 mass% or less,
A precipitation hardening stainless steel sintered body, characterized in that the value of δ defined by the following formula (1) is 10.0 mass % or more and 13.5 mass % or less.
δ=3(A+1.5B+0.5C)-2.8(D+0.5E+0.5F)-19.8・
...(1) A step of molding the compound according to claim 5 or the granulated powder according to claim 6 to obtain a molded body;
sintering the molded body to obtain a sintered body;
wherein the carbon atom concentration in the sintered body is lower than the carbon atom concentration in the precipitation hardening stainless steel powder.

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